1. Field of the Invention
The present invention relates to an image processing apparatus, an image processing method, and a computer program, and, more particularly to an image processing apparatus, an image processing method, and a computer program for making it possible to improve, for example, when predetermined signal processing is applied to an image, the gradation of an image obtained by the predetermined signal processing.
2. Description of the Related Art
FIG. 1 is a diagram of a configuration of an example of an image processing system in the past (a system refers to a logical set of plural apparatuses irrespective of whether the apparatuses having individual configurations are present in the same housing).
In FIG. 1, the image processing system includes an image-for-storage generating apparatus 10 and an image-for-display generating apparatus 20.
The image-for-storage generating apparatus 10 includes a quantization unit 11 and generates an image to be stored in the image-for-display generating apparatus 20.
The image-for-display generating apparatus 20 can be applied to, for example, a television receiver (hereinafter also referred to as TV (television)). The image-for-display generating apparatus 20 applied to the TV stores, for example, an image of a menu screen and a background image as some kind of background. The image-for-storage generating apparatus 10 generates an image stored by the image-for-display generating apparatus 20.
Specifically, a multi-bit image such as an image including 16-bit components of R, G, and B (Red, Green, and Blue) (hereinafter also referred to as 16-bit image) created by, for example, a designer as an original image of a menu screen using an image creation tool is supplied to the image-for-storage generating apparatus 10.
In the image-for-storage generating apparatus 10, the quantization unit 11 quantizes, for reduction of a volume and a calculation amount in the image-for-display generating apparatus 20, the 16-bit image, which is supplied to the image-for-storage generating apparatus 10, into, for example, 8 bits smaller than 16 bits. The image-for-storage generating apparatus 10 outputs an 8-bit image (an image including 8-bit components of R, G, and B), which is obtained by the quantization in the quantization unit 11, in an image file of a format such as PNG (Portable Network Graphics).
The image-for-display generating apparatus 20 includes a storing unit 21, a signal processing unit 22, and a gradation converting unit 23.
The storing unit 21 is, for example, a flash memory and stores the image file output by the image-for-storage generating apparatus 10.
Specifically, the image file output by the image-for-storage generating apparatus 10 is written (stored) in the storing unit 21 in, for example, a factory that manufactures the TV to which the image-for-display generating apparatus 20 is applied.
The signal processing apparatus 22 applies necessary signal processing to the 8-bit image of the menu screen stored in the image file stored in the storing unit 21 and supplies an image subjected to the signal processing to the gradation converting unit 23.
The gradation converting unit 23 gradation-converts the image from the signal processing unit 22 into the 8-bit image and supplies the 8-bit image to, for example, a not-shown display that can display the 8-bit image (hereinafter also referred to as 8-bit display).
Specifically, an image obtained as a result of the signal processing applied to the 8-bit image by the signal processing unit 22 may be an image including a lager number of bits than the 8-bit image. It is difficult to display the image including a larger number of bits than the 8-bit image on the 8-bit display. Therefore, the gradation converting unit 23 gradation-converts the image from the signal processing unit 22 into the 8-bit image.
In the gradation converting unit 23, dithering processing for adding noise to an image and then performing quantization of the image is performed as gradation conversion. In this specification, the dithering processing includes a dither method and an error diffusion method. In the dither method, noise unrelated to an image such as random noise is added to the image and then quantization of the image is performed. In the error diffusion method, (a filtering result of) a quantization error as noise is added to an image (error diffusion) and then quantization of the image is performed (see, for example, Hitoshi Tokay, “Yokuwakaru Digital Image Processing”, sixth edition, CQ publishing).
The gradation converting unit 23 performs gradation conversion when the image from the signal processing unit 22 is an image including a larger number of bits than the 8-bit image. When the image from the signal processing unit 22 is the 8-bit image, the gradation converting unit 23 directly supplies the 8-bit image to the 8-bit display.
The 8-bit image of the menu screen stored in the image file of the storing unit 21 is processed as explained above and displayed on the 8-bit display when, for example, a user performs operation to display the menu screen.